Pneumatic rubber tires for vehicular use conventionally have sulfur cured rubber treads. Such treads are typically composed of one or more sulfur curable, diene rubber-based elastomers.
Typically, quantitative inclusion of saturated, non-elastomeric, thermoplastic polymers in the diene rubber-based sulfur curable rubber treads is avoided, primarily because such saturated, thermoplastic polymers do not have sulfur cure sites and, thus, create uncured areas in the cured rubber tire treads which might degrade one or more desirable tire properties such as, for example, resilience, low heat buildup and resistance to permanent set.
It is recognized that, in one aspect, tire treads containing high density polyethylene, characterized by having a softening point above 275.degree. F. (135.degree. C.) has been taught for use as an additive (2-20 phr) in a tread cap designed to contact the road (U.S. Pat. No. 4,675,349), where the high density polyethylene is mixed at a temperature of about 200.degree.-240.degree. F. (93.degree.-116.degree. C.), the mixing temperature "being insufficient to significantly alter the size and shape of the polyethylene particles . . . " at column 6, line 32-34 of the aforesaid U.S. patent. The use of such a high density polyethylene is said to provide a tire with a "good balance of rolling resistance, skid resistance, wear and handling".
However, it is considered that, for some applications, it is not entirely desirable to use a blend of rubber and high density polyethylene.